1. Field of the Invention
The present invention relates to a liquid crystal display panel cutting system and a liquid crystal display device fabricating method, and particularly, to a liquid crystal display panel cutting system and a method thereof capable of preventing a cutting wheel from being damaged due to excessive cutting of a substrate by varying pressure and rotating speed of the cutting wheel which cuts substrates according to types of substrates to be cut.
2. Discussion of the Related Art
Generally, a liquid crystal display device provides liquid crystal cells arranged in a matrix form with corresponding data signals according to image information to display a desired image by controlling light-transmittance of each liquid crystal cell.
Accordingly, the liquid crystal display device is provided with a liquid crystal display panel in which liquid crystal cells are arranged in a matrix form; and a driver integrated circuit (IC) for driving the liquid crystal cells of the liquid crystal display panel.
The liquid crystal display panel is composed of a color filter substrate and a thin film transistor array substrate facing to each other; and a liquid crystal layer formed therebetween.
On the thin film transistor array substrate of the liquid crystal display panel, a plurality of data lines that transmit data signals supplied from a data driver integrated circuit to the liquid crystal cells are perpendicular to a plurality of gate lines that transmit scan signals supplied from a gate driver integrated circuit to the liquid crystal cells. Herein, the liquid crystal cells are arranged at crossings of the data lines and the gate lines.
The gate driver integrated circuit supplies the scan signals to the plurality of gate lines sequentially so that the liquid crystal cells arranged in a matrix form can be sequentially selected line by line. Also, the data signals are supplied to the liquid crystal cells of the selected line from the data driver integrated circuit through a plurality of data lines.
A common electrode and a pixel electrode are respectively formed at the inner sides of the color filter substrate and the thin film transistor array substrate facing to each other, thereby applying an electric field to the liquid crystal layer. The pixel electrode is formed to correspond to each liquid crystal cell formed on the thin film transistor array substrate. And, the common electrode is integrally formed on an entire surface of the color filter substrate. Accordingly, light-transmittance of the liquid crystal cells can be separately controlled by controlling a voltage applied to the pixel electrode under a state that a voltage is applied to the common electrode.
Like this, a thin film transistor used as a switching device is formed at the respective liquid crystal cells to control the voltage applied to the pixel electrode formed on each liquid crystal cell.
The plurality of thin film transistor array substrates are formed on a large mother substrate and the plurality of color filter substrates are formed on another mother substrate. Then, the two mother substrates are bonded, so that a plurality of liquid crystal display panels are formed at the same time to improve yield. Herein, a process for cutting the bonded substrates into unit liquid crystal display panels is required.
Generally, the cutting process of the unit liquid crystal display panels includes forming a scribing line at a surface of the mother substrate using a diamond wheel having a hardness greater than that of glass, and breaking the substrate by applying a mechanical force thereto. Hereinafter, a general liquid crystal display panel will be explained with reference to the attached drawings.
FIG. 1 is an exemplary view showing a schematic planar structure of a unit liquid crystal display panel prepared by bonding a thin film transistor array substrate and a color filter substrate of the liquid crystal display device to each other.
In FIG. 1, a liquid crystal display panel 10 comprises: an image display unit 13 having liquid crystal cells arranged in a matrix form; a gate pad unit 14 connected to gate lines of the image display unit 13; and a data pad unit 15 connected to data lines. At this time, the gate pad unit 14 and the data pad unit 15 are formed on edge areas of a thin film transistor array substrate 1 which does not overlap a color filter substrate 2. The gate pad unit 14 provides the gate lines of the image display unit 13 with a corresponding scan signal supplied from a gate driver integrated circuit, and the data pad unit 15 provides the data lines with image information supplied from a data driver integrated circuit.
On the thin film transistor array substrate 1 of the image display unit 13, the data lines having the image information applied thereto are arranged to perpendicularly cross the gate lines having the scan signals applied thereto. Then, thin film transistors are formed at each crossing to switch liquid crystal cells. Pixel electrodes are connected to the thin film transistors to drive the liquid crystal cells. A passivation layer is formed on the entire surface to protect the electrodes and the thin film transistors.
Also, color filters separated by a black matrix for each cell area are formed on the color filter substrate 2 of the pixel display unit 13. A transparent common electrode is formed on the thin film transistor array substrate 1.
A cell gap is provided between the thin film transistor array substrate 1 and the color filter substrate 2. The thin film transistor array substrate and color filter substrates are bonded to each other by a sealant (sealing unit) (not shown) formed at the peripheral regions of the image display unit 13, so as to be spaced apart from each other. A liquid crystal layer (not shown) is formed in the space between the thin film transistor array substrate 1 and the color filter substrate 2.
FIG. 2 is an exemplary view showing a cross-sectional structure of a first mother substrate having thin film transistor array substrate 1 and a second mother substrate having color filter substrates 2, wherein the first and second mother substrates are bonded to each other to form a plurality of liquid crystal display panels.
Referring to FIG. 2, each unit liquid crystal display panel has a thin film transistor array substrate 1 longer than the color filter substrate 2. This is because the gate pad unit 14 and the data pad unit 15 are formed, as illustrated in FIG. 1, at the edges of the thin film transistor array substrate 1, which does not overlap the color filter substrate 2.
Hence, the second mother substrate 30 and the color filter substrates 2 formed thereon are spaced apart from each other by a dummy region 31 corresponding to the protruding area of each thin film transistor array substrate 1 on the first mother substrate 20.
Moreover, the unit liquid crystal display panels are arranged so as to maximize the use of the first and second mother substrates 20 and 30. Although it depends on models, the unit liquid crystal display panel is generally spaced apart from each other at a distance corresponding to the area of the other dummy region 32.
After the first mother substrate 20 having the thin film transistor array substrates 1 is bonded to the second mother substrate 30 having the color filter substrates 2, a scribing process and a breaking process are carried out to individually cut the liquid crystal display panels.
The cutting process of the unit liquid crystal display panels will now briefly be explained.
FIG. 3 is a view illustrating an exemplary structure of a related art cutting apparatus used in the breaking process.
In FIG. 3, a related art apparatus for cutting a liquid crystal display panel may include a table 42, first and second mother substrates 20 and 30 loaded on the table 42 after completing the previous processes, and a cutting wheel 51 for processing the first and second mother substrates 20 and 30 and thus forming scribing lines thereon.
In the related art apparatus for cutting the liquid crystal display panel, when the first and second mother substrates 20 and 30, including a plurality of liquid crystal display panels, the first and second mother substrates 20 and 30 facing and being bonded to each other, are loaded on the table 42, the cutting wheel 51 positioned over the first and second mother substrates 20 and 30 moves in a downwardly direction, and then rotates under a particular applied pressure to the second mother substrate 30, to thus form a groove-shaped scribing line on the surface of the second mother substrate 30.
The scribing lines are also formed on the first mother substrate 20. That is, the cutting wheel 51 is used to process the first mother substrate 20 to form the scribing lines at the same positions as the subscribing lines 58 on the second mother substrate 30. Accordingly, in the related art apparatus for cutting the liquid crystal display panel, the first and second mother substrates 20 and 30 are processed separately to form the scribing lines thereon. Thus, the second mother substrate 30 is processed first using the cutting wheel 51. Thereafter, the first mother substrate 20 is processed using the cutting wheel 51 in a state that the first mother substrate 20 is laid upwardly by turning the liquid crystal display panel over.
Afterwards, the subscribing lines (i.e., scribing lines formed on both the first and second mother substrates 20 and 30) are pressed to divide the first and second mother substrates 20 and 30.
However, several problems may occur in the related art apparatus for cutting the liquid crystal display panel as follows.
In the related art apparatus for cutting the liquid crystal display panel, the cutting wheel 51 does not cut the first and second mother substrates 20 and 30 completely but just forms the scribing lines thereon. Other processes are further performed to completely cut the first and second mother substrates 20 and 30. That is, according to the later processes, the first and second mother substrates 20 and 30 are completely cut by applying an impact along the scribing lines formed thereon. Accordingly, the first and second mother substrates 20 and 30 are divided into the liquid crystal display panels.
Thus, forming the scribing lines is intended to prevent a defect from being generated when cutting the first and second mother substrates 20 and 30. That is, in the related art cutting apparatus, the first and second mother substrates 20 and 30 are processed according to separate processes to form the scribing lines on the respective first and second mother substrates 20 and 30. Pressure is applied to the first and second mother substrates 20 and 30 to thus cut them along their scribing lines at once. Thereby, dividing the first and second mother substrates 20 and 30. Accordingly, when the first mother substrate 20 or the second mother substrate 30 is processed using the cutting wheel 51, if the corresponding mother substrate is completely cut, an impact may be applied to the substrate, which faces and is bonded to the corresponding mother substrate, and thereby fabricate a defective liquid crystal display panel. Particularly, if the second mother substrate 30 is completely cut using the cutting wheel 51, when turning over the first and second mother substrates 20 and 30 bonded to each other, an impact may be applied to the first mother substrate 20, which may cause a defect.
In order to prevent such a defect, the scribing lines are separately formed on the first and second mother substrates 20 and 30, and then later processes are performed to completely divide the first and second mother substrates 20 and 30. Hence, the substrates 20 and 30 are not completely cut. Specifically, only the scribing lines are formed thereon by setting cutting conditions of the cutting wheel 51, for example, pressure applied to the cutting wheel 51, a rotating speed of the cutting wheel 51, or the like.
However, the mother substrates used in the liquid crystal display device fabricating process have various characteristics. In other words, because characteristics of glass substrate may be varied according to a type or fabricating company of the glass substrate, a size of the glass substrate, or the like, if another type of mother substrate is processed in an actual cutting process of liquid crystal display panel, the mother substrate is completely cut to thereby cause a defective liquid crystal display panel.